Conference Proceedings Paper
SUBCRITICAL REACTIVITY CALCULATIONS
37th Annual CNS Conference - 2017 June 04-07
E. Talbot (SNC-Lavalin)
Simulations of subcritical CANDU reactor cores show that both the dynamic and fixed-source reactivities are generally more negative than the eigenvalue reactivity, at least when solid rods are used to supply the reactivity suppression. Full-core reactor physics simulations using the different RFSP calculation methodologies (eigenvalue, dynamic, and fixed-source) are used to study situations in which these reactivity definitions differ significantly. It is found that the fixed-source and dynamic reactivities always match quite well but the eigenvalue reactivity can be significantly closer to criticality in core configurations with a large flux tilt. A transient that returns a highly asymmetric core configuration to criticality shows that the apparent additional shutdown depth seen in dynamic and fixed-source reactivity calculations coincides with a larger moderator poison coefficient. The dynamic, fixed-source, and eigenvalue calculations all predict a return to criticality, to within a small fraction of the delayed neutron fraction, at the same core configuration.
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